noun
1. usually hardcore ˈ ̷ ̷ˌ ̷ ̷ chiefly Britain : brick rubbish, clinker, broken stone, or other hard material in pieces used as a bottom (as in making roads and in foundations)
2. : an especially resistant or enduring structural and usually basic or central part of a larger entity: as
a. : the most militant, die-hard, or loyal element or nucleus of a group, organization, or movement
this group, whose hard core … is the trade unions — C.J.Friedrich
the party's hard core of stubborn ultraconservatives — New York Times
b. : a group of refugees or displaced persons not readily sponsored or resettled because of physical or other incapacities ; specifically : a group of refugees requiring institutional care wherever they go
hard-core cases — incurably sick people, bedridden old people, inevitable charges of the state — John Hersey